1. Field of the Invention
The present invention relates to an apparatus for processing input/output pulses to and from a microcomputer, particularly to a flexible input/output pulse processing apparatus suitable for use in a microcomputer for controlling various devices or apparatuses.
2. Description of the Related Prior Art
A typical example of conventional apparatus for processing input/output pulses (called an I/O pulse processing apparatus, hereinafter), especially a counter/timer, incorporated in a microprocessor is discussed in an article titled "Motorola's MC68HC11: Definition and Design of a VLSI Microprocessor" by James M. Sibigtroth (IEEE MICRO, February, 1984). The single-chip microprocessor discussed in the above article has an excellent function. However, in this microprocessor, especially in the I/O pulse processing apparatus associated with the microprocessor, the number of counter/timer registers, the number of capture registers each for holding the number of input pulses, and the number of compare registers each for determining the pulse width of a pulse output are all fixed. Moreover, the functions of these registers as well as the combination of counter/timer registers and capture or compare registers are fixed. Accordingly, in the case where the microprocessor is applied to the control of various devices or apparatuses, the counter/timer part of the I/O pulse processing apparatus will be deficient in selection of registers. Further, as to the arrangement of I/O pins as I/O terminals, only the output terminal of a specified counter/timer register can be selected from a plurality of terminals, but other terminals are fixed. Specifically, in a single-chip microprocessor, the number of I/O terminals is limited and hence it is desirable to be able to freely change the connection between counter/timer registers and I/O terminals.
In order to realize an I/O pulse processing apparatus suitable for controlling various devices or apparatuses by a microcomputer, the inventors have proposed an apparatus as disclosed in U.S. application Ser. No. 793,350 filed on Oct. 31, 1985, in which the numbers of counter/timer registers, capture registers and compare registers are freely determined and the connection between registers and I/O terminals (pins) can be arbitrarily changed. In the apparatus, however, since a task required for the I/O pulse processing apparatus must be instructed by a microcomputer associated therewith concretely and specifically to a great extent, the manner or form of I/O processings was not easy to be amended. Namely, it was limited to the manner or form prepared in advance, and therefore the flexibility of the apparatus was considerably poor.